This invention relates to a method for the alternate reversing or switching of two reversible and interchangeable regenerators, one of which has been heated by a hot fluid and the other of which has been cooled by a cold, other fluid.
Conventionally, after reversal, cold fluid is introduced into the heated regenerator, and hot fluid is introduced into the cooled regenerator. The hot and cold fluids differ not only in their temperatures but also in their chemical compositions. During introduction of the cold fluid into the heated regenerator, the hot fluid still present therein is mixed with the other fluid and entrained by the latter. The chemical composition of the other fluid to be heated, therefore, is different, directly after reversing the regenerators, from the composition of the other fluid prior to introduction into the heated regenerator. This, however, is a disadvantage and can lead to considerable disturbances in the course of the subsequent process steps.
For example, when using regenerator pairs for the cooling of hot flue gas from a combustion zone associated with, e.g., boilers, furnaces or reactors, with the simultaneous heating of the air of combustion, when switching over from flue gas operation to air operation, flue gas is briefly returned to the combustion zone before the air has displaced the regenerator content of its residual flue gas. For a short time, therefore, a flue gas-air mixture is fed to the combustion zone; so for a finite time period, combustion is impaired due to a decreased oxygen concentration.
In the case of large boilers, several parallel regenerator pairs may be required for reasons of economics (for example 3 to 4 pairs of dual-stream regenerators in a 300 MW power plant with 10.sup.6 m.sup.3 /h of flue gases). By timing the switching of the individual pairs so that there is little or no overlapping, it is possible--combined with bypass regulation--to suppress the fluctuations of quantity of combustion air and oxygen concentration, with certain limits. However, when using an air bypass stream, cold air that has not been preheated is briefly conducted to the combustion stage. Thus, uniform combustion of the fuel is disrupted, and this constitutes a considerable disadvantage, especially in light of the fact that regenerators are cycled every few minutes.